Field
The present disclosure relates to techniques for reflecting optical signals. More specifically, the present disclosure relates to a single-mode optical reflector based on a nanobeam cavity.
Related Art
Silicon photonics is a promising technology that can provide large communication bandwidth, large density, low latency and low power consumption for inter-chip and intra-chip connections. In the last few years, significant progress has been made in developing low-cost components for use in inter-chip and intra-chip silicon-photonic connections, including: high-bandwidth efficient silicon modulators, low-loss optical waveguides, wavelength-division-multiplexing (WDM) components, and high-speed CMOS optical-waveguide photo-detectors.
Nonetheless, a high-efficiency, single-mode light source for use in silicon photonics remains a challenge. One approach for implementing such a light source is a hybrid external cavity laser, in which a III-V material section is used as an electrically pumped optical gain medium, and a silicon minor is used as the other reflector in the external cavity, as well as an output coupler. However, it has proven difficult to implement an integrated reflector with a narrow bandwidth and a single mode.
For example, integrated ring-resonator reflectors have been demonstrated. However, ring-resonator reflectors have periodic reflection peaks as a function of wavelength, which can cause optical mode instability because of competing optical modes within the gain spectrum of the laser. Moreover, controlling ring-resonator reflectors can be complicated and the control often requires significant thermal tuning power. Furthermore, ring-resonator reflectors can have a large footprint, which reduces their pitch.
A distributed Bragg reflector (DBR) is another type of integrated mirror that reflects a single wavelength. However, a very weak modulation of the Bragg grating is needed for a narrow bandwidth, which usually requires a large number of grating periods that make the DBR undesirably long. Furthermore, while the combination of a ring-resonator reflector and a DBR can provide a narrow bandwidth and single-mode reflection, the resulting reflector typically has a large footprint.
Hence, what is needed is an integrated reflector without the above-described problems.